Abstract

A review has been completed of current and proposed processing technologies for nickel laterite ores. Although future supplies of nickel depend on laterite ores, their processing is inherently energy intensive and expensive as, unlike sulphide ores, they cannot be significantly upgraded, meaning the entire ore needs to be treated in the process. In addition, hydrometallurgical processes in particular have significant waste disposal problems. However, new technologies are being developed that are attempting to address the current processing issues, including some innovative processes that are in their early stages of development.

Smelting is a well known and proven technology for saprolite ores that is continually being improved. It is a high energy consumer and needs to be performed on a large scale to be cost-competitive. It remains the most popular option for large scale developments based on saprolite ores and accounts for a significant amount of nickel production from laterite sources.

High Pressure Acid Leach (HPAL) remains the process of choice for treating limonite ores, especially for large scale developments. It has the advantages of high nickel and cobalt recoveries and is applicable to a wide range of ores. However, the process does suffer from significant waste disposal issues.

Atmospheric and Heap Leaching. Smaller scale developments are being actively pursued based on Atmospheric Leaching (AL) or Heap Leaching (HL) technologies. These processes do not rely on autoclave technology and are therefore perceived to be less capital intensive and easier to operate. However, they still require significant investment in terms of infrastructure. Heap leaching is the option most investigated, whereas AL is gaining momentum for mixtures of limonitic and saprolitic ores. Waste disposal issues are again significant.

Downstream Product Recovery. The two main downstream processing technologies for nickel recovery from solution are mixed hydroxide precipitation and mixed sulphide precipitation. Refining to pure nickel and cobalt products is an option in the large scale HPAL projects.

NEW TECHNOLOGIESHydrochloric Acid Leaching has been investigated on a laboratory scale for some time based on the fact that the acid can be reformed from the waste liquor by pyrohydrolysis or, more recently, distillation. In order to be competitive, these processes require that acid usage is minimised. However, aggressive leach conditions with high acid consumptions are still required to give good nickel recoveries. In some processes, waste disposal can be minimised.

Bioleaching of oxide ores is a concept that is in its infancy, but does offer some advantages over conventional processes. The process uses organic matter to produce organic acids in situ that leach the ore, possibly by-passing the need for expensive mineral acids, and reducing waste disposal problems associated with current processes.